purpose of 90 degree gearbox on brush hog

[jhubert]

If building one from scratch for say a hydraulic powered application, what is the purpose of having that 90 degree gearbox in the system. Why cant you mount the hyd motor as a vertical shaft and skip that 500$ part? As long as there is a shear pin in the equation and as the operating speed is figured correctly (you wouldnt need to step up rpm in the gearbox) what else is the reason for it? I cant believe its to isolate the motor from taking hits because I work with alot of cast iron and it is brittle! And hyd motors are solid machined parts and only the oil cavity is hollowed out so they gotta be pretty tough.

[Farmerford]

Several skid steer mower manufacturers use a cast or welded bracket to hold a hydraulic motor on one end and a mower shaft on the other end apparently in separate bearings so that only the torque load is on the motor. I have never seen them for sale separately; perhaps you could buy one as a replacement part. But I suspect those brackets are expensive, because they are probably not produced in large quantity, and because you have to buy them as a part. By the time you include the bearings, seals, and shaft, they are probably not much cheaper than an after market Chinese gearbox, which I think sell for around $300. Then you have to buy the blade holder, etc., etc.

I built a hydraulic mower for the front end loader and after a reasonable amount of research I bought a used mower and connected a 540 rpm hydraulic motor directly to the gearbox input shaft. The mower came with "standard" tapered spline output shaft that accepts the "standard" blade holder/stump jumper. Now if I tear up a stumpjumper or bend the shaft, the replacements are fairly easy to find.

[77 Ford]

I think the purpose is much more basic, have to convert horizontal power into vertical.

I think all shock and hit loads would be transferred equally to everything up stream from the blades.

[Tigerhaze]

As 77Ford says, I would tend to think any change in stress from the vertical and horizontal portions of a gearbox are neglible because the shear bolt for PTO driven brush hogs for tractors are at the junction of the PTO shaft and gearbox and am not aware of a second shear pin or bolt within the gear box assembly. However I haven't specifically looked at this issue.

[jhubert]

After searching more and watching countless sales videos I found a few who have done just what I was thinking....mounted the hyd motor vertically and skipped the gearbox. I wonder if its a better or cheaper design. A few of the ones running the vertical design are up over 7k$ for a 6' brush hog

[Paul Buhler]

Hi: Just wondering.
Have you considered a flail mower like the Ford 907? They are relatively light, the 3pt hitch can be mounted "backwards" so the mower could mow in front of a machine, and a hydraulic motor could be mounted directly in line with the pulley's drive shaft in place of the 90* gearbox. I saw a few used 907s listed fairly inexpensively.
At the ski area where I used to work on trails, they use Aebi tractors with flails to mow the steeper slopes. They like that they can deal with waterbars, rocks, and other hard stuff better than a rotary mower. Google Aebi images to see some pictures of what I mean.
Good luck with your project. Paul

[jhubert]

Thanks a bunch Paul. I did some quick research and found they offer vehicles in the 60hp range and run 8' flails at 16gpm? Theres one video in particular on youtube showing one really getting into some 3" scrub threes and shredding it up good in two passes. I wasnt aware that they made rough duty knives but they sure do have it figured out!

[jhubert]

I found a used alamo 21' flail (three 8 foot pcs) with a bit of overlap for 400 bucks with the hydraulic motor still on it. Looks to be in useable condition for what I want. I downloaded the manual and it says the center pc is PTO driven and the wings are driven hydraulically which is done by a pump that the PTO also is powering that sends fluid power to a motor mounted on each wing. I thought sweet but in reading along I found it requires 60 PTO hp to run this whole attachment (all three units). It says the pump makes 84hp of fluid power. Now how do you take 60 mechanical hp and make 84 fluid hp? The nitty gritty is it requires 24gpm at 3600psi to run the motor. Im pretty sure I cant spare that out of my loaders pump. I believe 28gpm at 3000 is what the dealer told me my pump should provide.

[Paul Buhler]

I'd be worried running a flail that wide on a machine that's nominally 8 feet wide. The torque and racking strain on the loader arms and flail body will be considerable. A smaller flail would need somewhat less hydraulic power too JMHO. Paul

[Lavoy]

I could be wrong, but I seriously doubt you are getting anything remotely close to 3,000 out of your pump. The new gen wheel tractors with closed center hyd in the same years as your crawler topped out at 2,250 PSI.
Lavoy

[jhubert]

Maybe the service manager was guessing so I could leave him alone sooner but that's what he said. Wouldn't be the first manager full of bologna. I really liked Paul's idea with the flail mower tho. Lets say I had a system that would barely drive either mower....I would think the rotating mass of a 6' rotary mower would help operation more so then a flail, no?

And Paul, I failed to explain it but I'm only talking about using one of the 8' wings mounted to my loader arms. So cutting width would match track width, and one section still requires more than I got lol.

[Paul Buhler]

And Paul, I failed to explain it but I'm only talking about using one of the 8' wings mounted to my loader arms. So cutting width would match track width, and one section still requires more than I got lol.

Gotcha. Best wishes as you search for a good match. As you've noticed, flails generally use one of two types of cutters depending on the material being cut. The lighter paired angled steel ones work well on grass and brush up to small saplings. From what I've seen, the heavier cast or forged claw shaped flail takes on heavier stock, but usually they are found on a heavier and more power hungry machine.

When we cleared meadows, we usually hit the area with chain saws first, lopping the limbs that stuck up on the downed trees, then ran over the area with a flail multiple times at various speeds and depths of cut, until "just right". (these were rear mounted on 3 pt hitches)
A respect for the limits of the machine and a feel for what was going on kept things together - flails still broke off and things would bend from time to time.

Paul

[Lavoy]

Barely is barely, so no. Mass is irrelevant to the equation, any energy lost must be recuperated. Plus, if you can "barely" handle what you have, taxing the hyd system at that level will result in failure, catastrophic or otherwise in fairly short order. Factor in a 40 year old hyd system that was never designed to run orbital functions, and it is pretty much a guarantee. Also, just because your pump will put out a given flow, it by no means guarantees that your valve will flow that through any given single function, in fact very unlikely that it will.
When the Deere 8000 series large frame row crop tractors came out in the late 90's, with the high flow option we could get a little over 50GPM pump output, but somewhat over half of that at a single scv, and this is with a modern high pressure hyd system on an up to 210 PTO HP tractor. They also had an oil cooler that was probably equivalent to the radiator on your 450, and at that flow should have been running a motor sump return line to eliminate as much restriction and back pressure as possible.
Lavoy